I had constipation for a few weeks while I was ramping up on the SCD. Once my body got used to it, I was able to go regularly and have -- not to give T.M.I. -- really really satisfying BMs. There could be a number of reasons for your constipation:
1) Dehydration can cause things to slow down drastically
2) Strictures, scar tissue, and physical obstructions (I have very bad strictures, but they seemed to ease once I got on the SCD) If this is the case for you, then hitting your system with a lot of fiber while you are having a flare up can lead to big problems.
3) Lack of fiber. If you believe that this is the problem, try starting the SCD with just fruit, vegetables, and nuts.